People who have seen pre-release audience surveys say the CGI-animated sequel, which features the voices of Mike Myers, Cameron Diaz and Eddie Murphy, will likely sell about $90 million worth of tickets in the U.S. and Canada this weekend.

2007's "Shrek the Third" opened to $122 million, and 2004's "Shrek 2" bowed with $108 million. Both also debuted the weekend before Memorial Day.

The decline in expected opening-weekend revenue for the fourth installment actually understates the degree to which interest in the fantasy series appears to have waned. "Forever After" is the first "Shrek" movie to play in 3-D, meaning tickets in the majority of theaters will carry a surcharge of $3 on top of normal ticket-price inflation over the last several years.

"Shrek" has so far been DreamWorks Animation's most lucrative franchise. Since the original was released in 2001, the studio has launched other hits, including "Madagascar," "Kung Fu Panda" and March's "How to Train Your Dragon," though none are yet as big as the snappy take on classic fairy tales. DreamWorks is working on a "Shrek" spin-off, "Puss in Boots," for 2011.

Executives at Paramount Pictures, which distributes DreamWorks Animation movies, are hoping that "Shrek Forever After" will continue to play well for the next several weeks as no other family films are opening until Disney/Pixar's "Toy Story 3" on June 18. The studio believes the movie ultimately will gross at least as much in the U.S. and Canada as "Shrek the Third," which finished with $323 million.

DreamWorks Animation stock has fallen 4% this week as word has spread on Wall Street about the movie's expected opening.

Even if it comes in slightly below what tracking polls indicate, however, "Shrek Forever After" is certain to have the third-biggest domestic opening of all time for an animated film, behind its two predecessors, not accounting for ticket-price inflation.

Paramount is also expecting that, like the last two "Shrek" movies, "Forever After" will sell close to $500 million in tickets overseas. Although it is opening in nine countries, including Russia, this week, most moviegoers abroad won't see the film until late June or July, after the World Cup ends.

The only other movie opening domestically this weekend is "MacGruber," based on the "Saturday Night Live" skit that parodies the 1980s television show "MacGyver." Financed by Relativity Media's Rogue Pictures and distributed by Universal Pictures, the low-cost comedy is expected to open to about $10 million.

Also notable this weekend will be the performance of "Robin Hood." Universal and Relativity's big-budget movie starring Russell Crowe opened to a soft $36 million, but since it appealed primarily to adults, who often don't come out for a film's first weekend, it could decline less than 50% on its second weekend in theaters.